Many technologies for visible full color or monochromatic displays exist or are in development. Example technologies include Cathode Ray Tubes (CRTs), plasma displays, Liquid Crystal Displays (LCDs), Organic Light Emitting Diode (OLED) Displays, Field Emission Displays (FEDs), Surface-conduction Electron-emitter Displays (SEDs), and projection displays. With the exception of projection displays and LCDs that filter white backlight to create red, green, and blue light required for full color display, all other display technology relies on phosphors that emit specific colors (typically red, green, and blue) when energized by an electron beam, ultraviolet light, or electrical current.
In the case of the LCD, the white light is supplied by Cold Cathode Fluorescent Lights (CCFLs) or white LED backlights that employ phosphors excited by UV or blue light respectively. A LCD is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source. Each pixel consists of a column of liquid crystal molecules suspended between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. Without the liquid crystals between them, light passing through one filter would be blocked by the other. The liquid crystal twists the polarization of light entering one filter to allow it to pass through the other. By applying small electrical charges to transparent electrodes over each pixel or subpixel, the molecules are twisted by electrostatic forces and allows varying degrees of light to pass (or not to pass) through the polarizing filters.
In color LCDs each individual pixel is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters. A “blue” subpixel absorbs red and green, while a red subpixel absorbs green and blue, and a green subpixel absorbs blue and red light. Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel.
A conventional full color backlit LCD backlight has many sources of inefficiency:    1) The white light backlight is either a white LED or a fluorescent light source. The white LED is fabricated of an underlying LED chip, usually a “blue” 460 nm source and occasionally a 405 nm or 390 nm source. The 460 nm, 405 nm are 390 nm sources may emit with the respective wavelength of 460 nm, 405 nm and 390 nm, which normally may be referred to as short wavelength emission. The underlying LED chip is overcoated with a phosphor layer that converts the short wavelength emission emitted by the underlying LED chip to longer wavelength emission. Similarly, the fluorescent light source comprises an ultraviolet lamp coated with white light emitting phosphor. This conversion process is the first source of inefficiency that can degrade potential optical output power by 10-30%. The conversion process may be referred to as down conversion because shorter wavelength emission has higher energy comparing to longer wavelength emission.    2) The backlight is passed through cross polarizers that sandwich the liquid crystal layer. Cross polarizers eliminate ˜50% of the light for a pixel that is “on”. A pixel that is “off” eliminates all the light and therefore has 0% efficiency    3) The light is then filtered to leave only red, green, or blue per pixel, therefore a further ˜66% of the light per pixel is lost.
In total only about 12%-15% of the light generated by the “blue” underlying LED chip makes it though the LCD display and made available to the viewer.
Patent application numbers 20060238671, 20060238103, 20070007881, 20060244367, 20060274226, 20070058107 describe an LCD device where red, green, and blue emitting phosphors and nanocrystals are used in place of the conventional color filter and in conjunction with blue or ultraviolet backlight sources. However, because phosphors and nanocrystals do not have 100% quantum yield and because of the inherent overlap between the absorption and emission spectrum, the maximum amount of light down converted by the phosphors occurs at a phosphor concentration/thickness product where there remains significant bleedthrough from the backlight source. The addition of the residual backlight plus red, green, or blue down converted light may change the perceived color of the pixel and reduce contrast. In at least one patent application, the inventors added a filter to eliminate ambient UV light from exciting the phosphor layer but the filter did not necessarily filter out the residual light from the backlight source.
All the display technologies listed above including LCDs operate in the visible portion of the spectrum. However, there are many applications in the military, police, and fire rescue that require infrared displays which do not emit visible light and can only be observed with night vision goggles or short wavelength infrared and near infrared camera systems. There is also a need to be able to convert a visible emitting display to an entirely infrared emitting display.
Although there are numerous examples and types of visible emitting phosphors used in display technologies, there is a lack of inorganic, small molecule or polymer electroluminescent phosphors that emit efficiently in the infrared spectrum. While there are some examples of infrared photoluminescent cyanine dyes (indocyanine), those molecules are inefficient emitters and are unstable resulting in emission quenching over a period of minutes to hours.